Following completion of this chapter, student will be able to:
- Identify the different types of lasers.
- Explain the physical principles used to produce laser light.
- Contrast the characteristics of the helium neon and gallium arsenide low-power lasers.
- Analyze the therapeutic applications of lasers in wound and soft-tissue healing, edema reduction, inflammation, and pain.
- Demonstrate the application techniques of low-power lasers.
- Describe the classifications of lasers.
- Incorporate the safety considerations in the use of lasers.
- Be aware of the precautions and contraindications for low-power lasers.
LASER is an acronym that stands for light amplification of stimulated emissions of radiation.
Despite the image presented in science-fiction movies, lasers offer valuable applications in the industrial, military, scientific, and medical environments. Einstein in 1916 was the first to postulate the theorems that conceptualized the development of lasers. The first work with amplified electromagnetic radiation dealt with microwave amplification of stimulated emission of radiation (MASER)s. In 1955, Townes and Schawlow showed that it was possible to produce stimulated emission of microwaves beyond the optical region of the electromagnetic spectrum. This work with stimulated emission soon extended into the optical region of the electromagnetic spectrum, resulting in the development of devices called optical masers. The first working optical maser was constructed in 1960 by Theodore Maiman when he developed the synthetic ruby laser. Other types of lasers were devised shortly afterward. It was not until 1965 that the term laser was substituted for optical masers.1
Lasers have been incorporated into numerous everyday applications that range from audio discs and supermarket scanning to communication and medical applications.2 This chapter deals principally with the application of low-level lasers as they are used in conservative management of medical conditions.
A laser is a form of electromagnetic energy that has wavelengths and frequencies that fall within the infrared and visible light portions of the electromagnetic spectrum.1 Electromagnetic light energy is transmitted through space as waves that contain tiny “energy packets” called photons. Each photon contains a definite amount of energy, depending on its wavelength (color).
A laser consists of a gain medium, which is a material (gas, liquid, solid) with specific optical properties contained inside an optical chamber (Figure 13–1). When an external power source is applied to the gain medium, photons are released, which are identical in phase, direction, and frequency. To contain them, and to generate more photons, mirrors are placed at both ends of the chamber. One mirror is totally reflective, whereas the other is semitransparent. The photons bounce back and forth reflecting between the mirrors, each time passing through the gain medium, thus amplifying the light and stimulating the emission of other photons. Eventually, so many photons are stimulated that the chamber cannot contain the energy. When ...